This invention relates to a photoelectrically operated temperature measurement system more particularly, to a system for measuring temperature by utilizing the fact that the fluorescence in a fluorescent material correlates with temperature.
It has been conventionally known that the characteristic of fluorescence in a fluorescent material correlates with temperature. In the past attempts have been made for measuring temperature photoelectrically by utilizing this quality of the fluorescent material. The conventional temperature measurement system is as follows.
A fluorescent material is disposed in a temperature environment for objective measurement. Ultraviolet rays are irradiated to this fluorescent material to cause its excitation. As a light source of excitation for emitting the ultraviolet rays, a halogen lamp is used, and only the ultraviolet rays of the light beams from the halogen lamp are selectively extracted by using an optical filter. Fluorescence emitted from the excited fluorescent material is received by an optical sensor and an electric signal corresponding to fluorescent intensity can be obtained from said optical sensor. The correlation between the fluorescent intensity from the above described fluorescent material under excitation and temperature had been previously obtained. On the basis of this correlation, temperature of the fluorescent material, that is, the objective measurement temperature can be calculated from output of the above described optical sensor.
In this way, the temperature measurement system using a fluorescent material remarkably differs from a purely electrical temperature measurement system generally using a thermistor or thermocouple and the like in that a transmission part (called detection-transmission part) for sampling the temperature is purely optically constituted. The detection-transmission part, being optically constituted, presents the desirable effect of noninfluence by electromagnetic noise and measurement can be performed without trouble even under an explosive or metal corrosive atmosphere.
However, the above described conventional temperature measurement system, relating to excitation of a fluorescent material with ultraviolet rays, has not been generally put in wide use for the following reasons.
In the past, excitation with ultraviolet rays has been applied because many fluorescent materials show very high efficient fluorescent action by the excitation of ultraviolet rays. In a present instance, the simplest easy PG,4 source of ultraviolet rays is a combination of the above described halogen lamp and an optical filter. However using a halogen lamp as the source of excitation light causes many problems. A large amount of electric power consumption is necessary for a halogen lamp. A large amount of heat being generated from the lamp requires heat dissipating measures. Accordingly, the light source becomes very large in size and not suitable for long time use. Use of an optical fiber is not suitable for the light transmission device to guide ultraviolet rays from the lamp to the fluorescent material. Use of an optical fiber increases the flexability of use and is preferable also from the standpoint of noise resistance and corrosion resistance. On the contrary, as well known, a large amount of transmission loss of ultraviolet rays is inevitable in an optical fiber, and if ultraviolet rays of high energy are emitted through an optical fiber for a long time, the optical fiber undergoes a change in its glass composition resulting in coloring and deterioration of permeability. Further it is difficult to efficiently introduce widely dispersed light from the halogen lamp to a fine optical fiber. Thus, it is very difficult to irradiate ultraviolet rays from a halogen lamp efficiently to the fluorescent material through an optical fiber, and accordingly an optical fiber could not be used.